If each side of a square is increased by 25%, find the percentage change in its area.

Let each side of the square be a. Then, area = . $a2$
New side = $\frac{125a}{100}=\frac{5a}{4}$. New area =  $\frac{5a}{4}2$ =  $\frac{25a2}{16}$

Increase in area =  $\frac{25a2}{16}-a2=\frac{9a2}{16}$
Increase% =  $\frac{9a2}{16}*\frac{1}{a}*100$ % = 56.25%.